This is makeindex, version 2.15 [TeX Live 2019] (kpathsea + Thai support).
Scanning input file floss-arduino.idx....done (5 entries accepted, 0 rejected).
Sorting entries....done (11 comparisons).
Generating output file floss-arduino.ind....done (15 lines written, 0 warnings).
Output written in floss-arduino.ind.
Transcript written in floss-arduino.ilg.